Soap-making process



Nov. 2, 1948. a. B. BRADSHAW 2,452,724

SOAP-MAKING PROCESS Filed June 5, 1945 geo rge B- Bradshaw INVENTOR-ATTORNEY and treatment of oils and fats.

Patented Nov. 2, 1948 UNITED STATES PAT-NT orricE 2,452,72Q so rl yranmoraocnss,

George B. Bradshaw, Wilmington, Del; Application J u,r1e ,5, 1945 SerialN0...5Q7 61 .4 Claims. 1

This invention relates to the manufacture of soap. More particularly,this invention deals with that process of making soap wherein naturalfat-s, consisting essentially of glycerine esters of; higher fattyacids, are first converted into lower 'alkyl esters of said higher fattyacids, say the methyl, ethyl, propyl, or butyl esters, and the latterare then saponified with caustic alkali, liberating re spectivelymethyl, ethyl, propyl, or butyl alcohol.

The foregoing process was referred to in U. S. Patent No. lfldlflfi-i ofJoel Starrels, and described by me jointly with Walter C. Meuly in U. S.Patent No. 2,271,519. Certain modifications and improvements thereof arefurther described and claimed in U. S. Patent No. 2,360,844 by the twolatter inventors. This process has numerous advantages over the oldprocess of treating the glyceride of a higher fatty acid directly withcaustic, among which is simple recovery of the glycerine by-product andthe removal of impurities at the start instead of at the end of the soapprocess. The prior patents mentione above were concerned primarily withprocedures analogousto the traditional practice employed with the oldprocesses, which procedures I-haye found possess several inherentdisadvantages which reduce the economy-thereof.

It is accordingly an object of this invention to overcome thedisadvantages inherent in the lower alkyl soap process as heretoforedescribed. Another object of invention is to provide a practical,continuous method for carrying on the foregoing soap process on acommercial scale. Another-object is to provide a, process which canutilize lower alkyl esters of fatty acidswhich contain up to 10% freefatty acid, which may often be desirable, especially where esters madeby an acid catalyzed exchange are available. A still further object isto provide for the economic recovery of the alcohol liberated. A stillfurther object is to produce soap in a form which lends itself readilyto plodding. A further object is to provide a method of manufacturewhich is free of objectionable foaming. A further object is to providefor the rapid initiation of thereaction of the starting materials andfor their simple water-in-oil emulsification Without having to supplysteam for this purpose, or expensive outside mechanical energy. Afurther object is to dispense with heating, and yet deliver-a cooleddried soap. Another object is to provide an apparatus of general utilityin soap manufacture It is a further object to produce soap of acharacter not hitherto attained, to-wit containing' fats saponified 993%and no more than 0.1% free caustic, the soap being ofgan unexpectedlyfine odor and as desired containing less than 0.05% sodium chloride, noglycerine and less than .05% free fatty acid.

above paragraph is by no means exhaustive of the numerous objects andadvantages of my invention, as will become evident later.

Among previousprocesses for making soap-from lower alkyl esters of fattyacids is that disclosed in S. Patent No. 1,701,703 of Joel Starrels,Where the alcohol produced in the saponiiication isremoved as formed. Insuch a procedure there is great difiiculty because of foaming. Alsoexcess 1-yemust be used to complete the saponification. Since there isno separation over a. nigcr, as in the ordinary boilingprocess, aneutral soap is not produced. The other main difficulties-wi h theaforesaid and all soap processes are the time and energy required. Ihave outlined below several discoveries about soap manufacture, which iftaken. into account, make possible the rapid manufacture of dry,neutral,salt-free soap from lower alkyl esters, with little-energy input.

First, the conversion ofan ester of a fatty acid to the sodium orpotassiumsalt of that acid, that is to soap, really deports itself asthough -it con sisted of two steps. In the first step there is ahydrolysis or taking up of water and splitting of the ester, and in thesecond step there is a hentralization by the caustic alkali of the freefatty acid formed bythe first step, and the consequent release of water.The hydrolysis step and the neutralization step are exothermic.Theoretically about 75,000ca1ories per kilo are set free on treatmentwith caustic soda. Further, if these steps occur molecule by molecule,the reaction becomes of the chain type in that energy is passed on toadjacent molecules without first becoming evident as heat. In such areaction the speed I ecom s extremely high. from aconsideration of theabove it "is seen that if some heat is at the start, the reaction underproper conditions can bemade very rapid.

Second, to enable the inception of the rapid chain type reaction itappears necessary that the water solution of caustic alkali be finelyemulsi fled in the fat, that is, that a water-incil-type emulsion beformed. This is really a corollary. of the first proposition in thathydrolysis water must be in the fat in the presence of a fat splittingcatalyst, i. e., caustic soda. On mixing fat and a solution oi causticsoda to produce soap the lye often causes a graining out of thesoap justformed and causes a breaking of the emulsion essential to the react-ion.The phases must then be reunited by mechanical working under addition ofheat. As the grained soap is present in discrete particles of lowspecific heat, it is slow and difficult to get the reaction startedagain. This breaking of the emulsion is a function of temperature, andconcentration of the reactants. The higher the temperature the morelikely is the emulsion to break, but the greater the saponification theless likely it is to occur. Also the more water there is present, thelower the temperature at which the emulsion will break. To secure thewater-in-oil-type of emulsion it is necessary that there be present acertain amount of concentrated soap. This means concentrated alkali mustbe used. The concentration of the alkali, if a caustic soda solution,should not be much below about 35%, and the temperature of making theemulsion should be from a little above the melting point of the fattymaterial to about 65 C. On first mixing methyl esters of a fatty acidand caustic alkali, an oilin-Water emulsion is formed which is renderedunstable and finally inverted to a water-in-oil type as theconcentration of soap becomes greater. A favorable content of soap forthe waterin-oil type of emulsion is from 10% to 25%.

The formation of the first soap is aided by the presence of anemulsifier such as lecithin or by free fatty acid or by soapsaponification catalysts, such as a phenol or fat-splitting catalyst.Unless properly handled a content of free fatty acid above 3% becomestroublesome, because saponification becomes so rapid, clots are formedwith consequent non-uniform saponification. The belief that water mustfirst be present in the fatty ester before s-aponification can startagrees with the fact that the soap catalysts phenol and thymol are veryweak oil soluble acids which give off and take up water in the presenceof caustic soda and under varying conditions. The lecithin and thefat-splitting catalysts tend to form water-in-oil emulsions. Also, thefact that saponification is aided by pressure and hindered by vacuumagrees with the theory that the saponification occurs in a waterin-oilemulsion.

Third, in the presence of alcohol of high enough concentration a neutralsoap can be made. In any ordinary saponification in the presence ofwater there is an equilibrium short of complete sap-onification due tothe fact that soap dissociates in water solution. In order that all thefat be saponified, from 5% to excess alkali is required. This is thecase in every soap process using water as a medium. In the boiledprocess most of this excess lye is removed in that the batch is allowedto form a 70% soap 30% water phase over a niger. In the cold processthere is always used either an excess of caustic lye or an excess offat. If there is an excess of fat rancidity is likely to develop in thefinished soap since a good stable soap should not contain over 0.1%unsaponified fat. Accordingly, completely saponified neutral soap can besecured from lower alkyl esters of fatty acids, say methyl esters, bycompleting the saponification without removing the alcohol formed and byThis means the re- 7 plete saponification and furthermore this nearlycomplete saponification will gradually complete itself in the space of24 to 72 hours at ordinary temperatures while the soap is being workedup or even in storage as a finished product.

As hydrolysis is continually proceeding in the soap reaction there willbe a certain amount of free fatty acids present at the end if there wasan excess of oil at the start. Any superfatting secured by using anexcess of fatty material at the start will therefore entail the risk ofproducing an unstable soap. This is because most soap making fats wouldyield some unsaturated acids which, if left in the free state in thefinished soap, would tend to quickly decompose. Superfatting if desired,may be produced by adding an easily saponified ester of a saturatedfatty acid, such as palmitic or stearic acid for instance pure methylstearate or mono stearyl glyceride, at the end of the reaction. Suchaddition can also be made as a buffer to compensate for any error in theamount of caustic alkali or to allow for an excess of caustic purposelyused. The lower the temperature at which the soap reaction is carriedout and the quicker it is finished the less hydrolysis of excess esterswill occur.

Another very important reason for keeping the temperature down duringthe reaction is to obviate oxidation. Other factors producing oxidationare presence of air and of oxidation catalysts such as salts of iron andcopper. The starting materials should not contain air, and air should beexcluded in the subsequent treatment.

It is particularly important also from the odor angle that the reactionsincident to high temperaturedo not occur. The cost of perfume in atoilet soap ranges from one to two cents per pound of soap. A properlymade soap from, say, methyl esters of fatty acids requires very littleperfume.

In the light of the above it is now possible to detail a practicalcontinuous pressure soap process. The objections to such a processhitherto have been the high temperature, from 200 to 300 (3., requiredto attain the necessary speed of reaction, and the excess of alkali inthe product.

In general I operate my lower alkyl soap process in a special three stepprocedure under autogenous pressure and temperature, which arecomparatively low, and under substantially adiabatic conditions wherebyall the reaction gases and practically all the heat developed in theprocess are retained in the reaction mass itself or in the reactionvessels until the third or cooling step.

In a practical application of my invention, a monohydric alcohol esterof a higher fatty acid, for instance the methyl ester obtained byalcoholysis of a natural fat (a glyceride) by the aid of an alkalinecatalyst according to U. S. Patents No. 2,360,844 and No. 2,271,619, orWith the aid of an acid catalyst, is partially reacted with concentratedaqueous sodium hydroxide solution in a suitable vessel or apparatus,where at the same time the reaction is initiated and a water-in-oilemulsion is formed. This emulsion is pumped into a long water jacketedand heat lagged pipe which constitutes the main reactor. The length ofthis pipe is governed by the reaction time desired and the conditions ofheat interchange to the water jacket, and is usually about feet. Thediameter of the pipe determines the output capacity. The reaction in theemulsifier is spe ded by adding heat preferably by interchange from thewater which as passed through the water jacket of the lon reaction pipe.The reaction having started in the emulsifying apparatus and being about25% completed therein, continues in the long pipe reactor as thematerials move to the discharge end, the methyl alcohol liberated andabout half the heat generated being retained thereby maintaining themass in a plastic fluid state and under pressure. The heat transferconditions in the reactor'are such that the reaction has passed thecritical emulsion breaking stage before the temperature is reached tocause such breaking.

At the end of the reaction pipe the nearly com-' pletely saponifiedmaterial contains enough heat to dry it to any degree depending on theabsolute pressure into which it is discharged. The heat is suificient,if 50% caustic soda has been used for saponification and if the startingmaterials were introduced at a temperature of about 40 C. and if theheat losses have not been above about 20%. The system as justdescribedenables the ready addition of more heat by means of the heat transfermedium, if it is needed because of the use of more water in thecomposition or to speed up the reaction, or in the presence of otheringredients.

At the discharge end there is a throttling release so that the desiredpressure is maintained in the reaction pipe. The discharged material maybe passed through a spray nozzle into a vacuum chamber wherein a vacuumof about 27" of mercury is maintained, with the result that as soon asthe plastic soap emerges from the nozzle methyl alcohol and water areevaporated, pufiing up the residual mass to a flaked porous solid. Thegaseous methyl alcohol and water are led off through the top of thechamber through filters to a condenser, while the cooled fluffy soapparticles of desired moisture content drop to the bottom of the chamberand may be continuously led off to a plodder, and eventually pressedinto cakes. Alternatively the discharge may be to a continuous cooler toproduce either puifed up or solid soap.

The above described practical application details a three step process.In the first step, in the space of five to ten minutes and Without lossof heat, there is continuously produced a wateri-n-oil type emulsionhaving a temperature of about 35 to 65 C. and of about the followingcomposition, if 50 caustic soda was used:

Per cent Methyl esters of fatty acids 55 to 63 Soap 24 to 16 Causticsoda 7.5 to 8.5 Methyl alcohol 2.5 to 1.5 Water 11 to 11 In the secondstep this emulsion is allowed to continue to react for up to 20 minutesunder a pressure of about thirty pounds absolute and a temperature ofabout 100 C. to nearly complete saponification. In the third step thereacted mass is continuously discharged from the reaction pipe, when itmay be handled in various ways including that of spray drying under avacuum.

I shall now by reference to the accompanying drawing describe apparatusparticularly suited for carrying out my invention. Referring to, thedrawing, the tank 3 contains a lower alkyl ester of higher fatty acidssuch as liquid methyl; esters of. tallow. n e ank I a sa ifyine ge 6.such. as. 50%. caustic soda solution. These. tasks are advant geouslyheated and: laggedso as; to s pply ma r ls. of a uniform desiredtempera:ture. Valves 2 and land pipes H and 1:8 connect the bottoms of: tanks I,and 3 t0 pr portionine feeding devices 5 o-f; any; one of the suitable.typeswell known to the art. The oil and caustieare continuously fed tothe circulating stream of p t fly' a t and; emu sified mat rial; y in s9 andzo. This streemof art al y reacted; a terial is kept in circulationby pump- 6 which is o such s that; t handles m t ial a about 10 timesthe rate it isifed by the two prop r-tione ins feeders hestr mi o r i lr a d ma: ter al is forced by nur fi. hrou h: th turbulent flow pip s Te ys m s ie d ir. L he contents of s; irculat g s s em just. de cribedare h that e. bu of the actants spends about five minutes circulatingthrough the tu;r. bulent flow p es. a d: he. pu p 6-v Atthe same timethis material is circulated, it; is subjected to at n action; o he hearansfer medium Which is, n on a down th ou h the jacket I. This flow issuch that at leastno heat is removed from the circulating materials.Con: tinually there is being pumped off from this syst m th ou h p pe byu p 8 r all e.- acted material equivalent to the teed .bytheproportioning feedersS. Pump 8 feeds partially reacted emulsified andhot material to the jacketed reaction pipe 8. In the jacket of pipe 9and counter current to the flow of the reacting material flows the heatexchange medium driven by pump it. Ifhis medium flows from the; jacketof pipe 9 through pipe 22 to jacket 1 and then by pip 3 t lat n p mp itand th n by P 24 to jacket of pipe 9. Pipe 24 may pass through a heatexchange system for either lowering or raising the temperature of theheat exchange medium. The reacted material discharges through throttlingpump [.0 by which the desired pressure is maintained in the reaction.pipe 9: The reacted mate-rial is forced through pipe 2 5 and spraynozzle II into thev drying towen k2 from which the gases are suckedthrough outlet M by a vacuum apparatus which maysconsist of dustcatchers, condensers, receivers and. vacuum pump. The product falls tothe bottom of the tower l2 and is continuouslyrernoved either by thesoap plodder l3 or a sealed discharge I5. Additions to reacted streamcan be made-'by a o po t ne fe der: ah ad. o p mp The heat transfermedium circulating through jackets of the reaction pipe and theemulsifier y not alway e essentia to e. pro es rom h m c tandpo nt. a wlj fs n rom. a consideration of the heat, balance which follows inExample II below. Without great inconvenience these jackets could beinsulated and any heat found necessary be supplied at tanks 1 and 3'.

To make the invention, clearer specific exam,- pies follow. I

Example I Me ill es er Glycerides Free, fatty acids 6 inirea'ction pipe9.

V 5732 15 of 50% lye.

'The theoreticalamount of caustic soda 100% required to saponify this is13921bs.'or 2784 lbs. of 50% caustic soda solution. About 20 lbs. extralye was used. Tank-3 was charged with the l0,000'lbs.'methyl estersandcontents brought toa temperature of 40 C. Tank I Was charged with the2800 lbs. caustic soda solution which was brought to a temperature of 25C. The proportioning. feeders 5'Were adjusted to feed 28 lbSLOf.thecaustic'lye and 100 lbs. of the methyl 7 esters every 12 minutes.The temperature of the wat'er in the heat exchange medium system wasbrought to 105 C. and the water circulated by ump 16} at a slow rate.operating at such a rate that it would handle Pump 6 was started5,000-lbs. perhouriof material and pump 3 was adjusted tohandle 640 lbs.per hour orat such a rate that noqpressure'would be built "up in thefeed to pump 5. With the air release cocks open at the top of turbulentflow mixer the feed was started from the proportioning feeders and pump8 started. As soon as system of pump '6, was filled'sam'ples of theemulsion were taken for-quick analysis and control of the proportions;Pump 10 was started similarly to 1911111105}, and so as'to' maintain apressure of aboutl5 lbs. gage ber 10 in which was maintained a vacuum of27. The sprayed soap was found to be cooled to a temperature of 50 C.and contained 3% methyl alcohol and 8% water. 7 It was plodded topellets and" stored for two days'and then milled and fplodded to barsand cut and stamped to cakes. The finished "soap contained 05% freecaustic ysoda'and less than 0.15% methyl alcohol. 1

Example II,

, Similarlywere treated 19,500 lbs. of methyl esters of mixed'tallow'andcoconut oil contain-, ingabout 7.5% glycerides and having asaponification number. M20537- Hence they required 2866 lbs. 100%caustic soda for saponification or V After saponifi'cation there wasproduced a mixture containing? 20,055 lbs. (9050'ki1o's) of soap figuredas an- I hydrous 7 169'lbs. (77 kilos) of glycerine 2,134 lbs. (966kilos) of methyl alcohol 2,866'lbs. (1300 kilos) of water This mixtureat the spray nozzle had a, temperature of 105 C. and the dried cooledmaterial had altemperature of position: I

I r u a Per cent Soap, 20,055 (9050 kilos) 87.33 Glycerine, 169 (77kilos) .73 Methyl alcohol, '658 (299 kilos) 2.87 'Water, 2,082 (944kilos) 9.07

There was evaporated 667 kilos of methyl alcohol and 356 kilosof water.The heat required to do this is j r I v I Calories 667,000X250166,200,000 356,000x540 192,240,000

. A sample taken ahead of 'pump 10 showed more than 95% reacted. Pumpill'fed the spray nozzle which sprayed into cha'nh 50 C. and thefollowing com- I Material Kilos V 0. Drop Calories Soap"; 9,050 0.7 55348;l00,000 Methyl alcohol and glycerino. 1,043 0.57 55? 32,640, 000Water 1,300 1.00 55 I 71, 500,000

In fdropping from a temperature of 105 C. to 50 C. the soap lost thisheat:

.In' the above batch 19,500 lbs of fat or-8844 kilos were saponified.The heat set free was 08,844,000 75 equals 663,300,000 calories. The

heat needed by the process was as follows:

It is evident that without the addition of outproportioners 5.

sideheat the temperature will not'reach 110 C.

' If steam costs per 1000 lbs. and there is 'obtained for heating 320calories er gram then 2,000,000 calories are worth 1 cent. If about400,000,000 calories were put into the process of Example'II the soap atspraynozzle would have a tcmperature o'f 155 C. and no vacuum would berequired to dry it. The sprayed soap how ever would have a temperatureof about C. j

and require cooling. The quality of the soap would not be as good asthat made atthe lower I temperature. 'Considering all factors thetemperature should be kept under C.

' Example IIIj' 10,000 lbs. of methyl'esters of iattyacids whichcontained 4% free fatty acid and about 28% methyl oleate and had asaponification value of 7 192 were similarly treated with about 3%excess or 3150 lbs. of 45% oausticsoda lye. The temperature in thereaction pipe was made to go to 140 C. by using outsideheat on thesystem.

*Just ahead of pump 10 therewascontinuously forced into the reactionstream a supply of liquid mono-stearic acid ester of glycerine equal toup i 1.5% of the mixture passing. The vacuum in the spray tower was heldat about 20" of mercury.

The finished soap, when analyzed two days later,

showed less than 0.1% free caustic alkali an less than 0.1% free fattyacid.

Example 11/ There was similarly treated a mixture of 97001 lbs. methylesters of tallow and 300 lbs. stearic acid. The tallow methyl esters hadan acid value of 5.7 and a saponlification number of 194. The causticalkali used was 3570 lbs. of a solution containing: i

. Pounds Potassium hydroxide 1940 Potassiumcarbonate .1 60

Water 1570- 7 t V 3570 The fat and the alkali had both been brought to atemperature of 45 C. before feeding to the a a The product from thereaction pipe 9 was fed directly to a cooler instead of to the spraytower.

Itis plain-from the above that the procedure for initiating the reactionmay vary widely. However, the factors of especial moment have beendiscussed and their application is illustrated in the examples. Thesimplest and easiest Way of insuring the proper initiation is to havepresent a certain amount of free fatty acid and to have startingmaterials at about 40 C. Some alkyl esters like those from coconut oilwill generally start very readily at room temperature. However, a verypure dry alkyl ester will not start readily. This is because thenaturally occurring lecithin emulsifier and the 0.1% to 0.2% waterusually present in seed oils are absent.

Many times it will be desired to add to the fat and alkali otheringredients. As these other ingredients will have a certain specificheat, there should be compensation in the heat balance for theirpresence. In general there should be enough total heat in the reactedmass so that its temperature reaches about 100 C. Example IV illustratessupplying outside heat. In this example the starting materials wereraised to 45 C. This was advisable because of the extra water present inthe caustic potash solution over that which would have been present ifcaustic soda were used.

Above I have given preferred examples of procedures. However, it is tobe understood that the invention includes variations within the scope ofthe claims which follow.

I claim:

1. A continuous process for producing soap, which comprises continuouslyforming a waterin-oil type emulsion by continuously adding approximatelystoichiometrical proportions of a concentrated, aqueous, caustic alkalisolution and of lower alkyl esters of higher fatty acids to an agitatedbody of such an already formed emulsion maintained at a temperature ofabout 35 to 65 C. and containing from to 25% of soap, passing thisemulsion at the rate it is formed through an enclosed space in which itis maintained at a temperature of from about C. to below C. underautogenously developed pressure, until nearly complete saponification ofthe fatty acids has taken place, and then reducing the pressure on thereaction mixture as it emerges from said enclosed space sufiiciently toevaporate off the major part of the lower alcohol and a substantial partof the water present therein, whereby said reaction mixture is cooledand a solid, soap of excellent commercial purity is obtained.

2. A process as claimed in claim 1 wherein the reaction mixture, as itemerges from the enclosed space, is subjected to spray drying undersubatmospheric pressure.

3. A process as claimed in claim 1 wherein there are added to thereaction mixture shortly before it emerges from the enclosed space a fewper cent of an easily saponified ester of a fatty acid of the groupconsisting of palmitic and stearic acid.

4. A process as claimed in claim 1, wherein methyl esters of higherfatty acids and a caustic soda solution of about 50% concentration areemployed.

GEORGE B. BRADSHAW.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,831,610 Shuck Nov. 10, 19312,299,603 Thurman Oct. 20, 1942 2,360,844 Bradshaw et al. Nov. 14, 19442,362,734 Ward Nov. 14, 1944 2,383,631 Trent Aug. 28, 1945 FOREIGNPATENTS Number Country Date 118,100 Australia Feb. 3, 1944

